The long-term goal of this work is to improve human health by enabling the discovery of disease-causing mutations. Many human diseases, including cancer, are ultimately caused by mutations in specific genes. Discovery of these genes is a critical step in improving detection and diagnosis of disease, as well as for the design of molecularly-based, targeted therapies. However, disease gene discovery is hampered by the difficulties of working with human populations and by the low penetrance of many disease-causing alleles. To improve disease gene discovery, we are using the zebrafish, an excellent model of human diseases including cancer, microbial pathogenesis and birth defects. Previously, we used forward genetic screens to identify gene mutations that cause increased cancer susceptibility in zebrafish. We and others have also shown that transgenic expression of specific human disease alleles makes zebrafish susceptible to the relevant human disease. These "susceptibility strains" generally require a "second hit"-a mutation at a specific locus-to manifest disease, and thus could be an invaluable resource for identifying critical disease- modifying genes in human disease. Progress in using the susceptibility strains for gene discovery is hampered by the low penetrance and long latency of disease, and by the lack of zebrafish models for epithelial cancers, the most common cancers in humans. We have successfully used haplotype mapping to identify a low-penetrance, adult onset disease gene causing testicular tumors in zebrafish. Here we propose to establish a robust, user-friendly haplotype mapping panel as a resource for the entire zebrafish community. Taking advantage of this panel and the zebrafish separase cancer-susceptibility strain, we will identify novel gene mutations responsible for epithelial carcinogenesis. The availability of haplotype mapping methods and these epithelial cancer strains will significantly expand the power of the zebrafish for human disease research. PUBLIC HEALTH RELEVANCE: More than half a million people die of cancer each year in the US, and better treatments are needed. To discover the genes mutated in cancers and allow the development of more effective therapies, we are using the genetic vertebrate model system, the zebrafish. In this proposal we describe methods to significantly increase the efficiency of cancer gene discovery in zebrafish and the generation of zebrafish that accurately model human cancers.